A spreading device, such as a trawl door (1), comprising frames (2, 3) defining a top and a bottom edge of the door (1) and a middle frame (4) positioned between the frames (2, 3) thereby establishing an upper and lower section； lower proximal and distal panels (5, 6) are provided in the lower section as well upper proximal and distal panels (7, 8) are provided in the upper section. The panels (5, 6, 7, 8) being of aerofoil construction. Lower flaps are (9) mounted under or on the distal panels (6, 8) and upper flaps (9') are mounted on the proximal or mesial panel (5, 7, 10, 11). The flaps (9, 9') are connected to driving units and adapted to be controlled remotely. The lower and upper distal panels (6, 8) have a distal surface (6', 8') rendering them hollow, wherein the lower flaps (9) constitute a part of the distal surface.
